Re: kaslr: better rng

[<Paul.Koning%dell.com@localhost>]

> On Nov 6, 2017, at 12:51 PM, Maxime Villard <max%m00nbsd.net@localhost> wrote:
> 
> Le 06/11/2017 à 18:28, Thor Lancelot Simon a écrit :
>> On Mon, Nov 06, 2017 at 07:30:35AM +0100, Maxime Villard wrote:
>>> I'm in a point where I need to have a better rng before continuing - and an
>>> rng that can be used in the bootloader, in the prekern and in the kernel
>>> (early).
>>> 
>>> I would like to use a system similar to the /var/db/entropy-file implementation.
>>> That is to say, when running the system generates /var/db/random-file, which
>>> would contain at least 256bytes of random data. When booting the bootloader
>>> reads this file, can use some of its bytes to get random values. It then gives
>>> the file to the prekern which will use some other parts of it. The prekern
>>> finally gives the file to the kernel which can use the rest.
>> What is the reason for using only part of the file, in any application?
> 
> I meant to say that the components don't take random values from the same
> area in the file, for them not to use the same random numbers twice.

Yes, that's critical if the other sources of entropy aren't sufficient by themselves.  Then again, if they are, there is no reason to bother with this file in the first place.

If you think you need this file, I would argue there should be two: the current entropy file for the kernel to use, and a separate one generated from a different chunk of random bit stream, exclusively for the use next time by the bootloader.

	paul